1. Field of the Invention
The present invention pertains to the field of digital data transmission. More particularly, its object is a method for the transmission of this type of data in messages organized in frames, and the device for using this method.
A network or chain for the conveyance of digital data generally requires several transmission media, each with specific characteristics: radio links, cable links, optic fiber links etc.
Microwave radio links are known to be vitiated by a relatively large number of errors, especially under certain limit conditions such as limits of range, fading due to mobility or atmospheric conditions or, more generally, to the environment, interference etc. Furthermore, such radio links can be affected for long transmission periods, especially for satellite links or links requiring relays. The distribution of errors combines a distribution of isolated errors and a distribution of errors in groups.
2. Summary of the Invention
By contrast, wire type or optic fiber type links are affected by a far smaller rate of errors.
The object of the present invention is a method for the transmission of digital data by messages organized in frames, providing for the transmission of this data swiftly and practically without residual errors, even when the conveying network or chain uses poor-quality links or modifies the transmission chain. This type of modification or "reconfiguration" of the transmission chain is reflected in breaks with or without loss of information.
To obtain this result, the data-transmission method according to the invention can be adapted in its characteristics to the quality of the link: it combines several techniques for the correction and/or protection of transmissions, this combination being suited at each instant to the quality of the link. These techniques which are known per se are chiefly:
The use of error detecting/correcting codes, the errors being detected and corrected by self-correlation; PA1 The repetition of the frames transmitted; PA1 The interlacing of the frames transmitted; PA1 The selective re-transmission of poorly received frames. PA1 The transmission, by the receiver station, of acknowledgment frames, in which, for a command message, the nature of the command is retransmitted to the sending station and, for a data message, the numbers of the properly received data packets are retransmitted to the sending station, PA1 And gives rise, upon the reception of these acknowledgment frames by the sending station, to the repetition of the command message if the corresponding acknowledgment message is not received and to the selective repetition of the frames made up of data packets, the numbers of which have not been detected in the acknowledgment frames.
However, according to the invention, these various characteristics are combined to obtain, at each instant, the highest possible efficiency of transmission and the greatest possible speed compatible with this quality at tht instant.
The invention comprises a method for the transmission of data by command messages or data messages comprising frames, on duplex links between transmitter-receiver stations, wherein a sending station in the transmitter position transmits, in each command message, a packet of data comprising the nature of a command and the corresponding data and, in each data messsage, frames made up of N packets of information each comprising a packet of data and the associated order number, wherein the transmission of each message before the transmission of the following message by the sending station gives rise to:
Another object of the invention is a device for the application of this method, the transmitting and receiving parts of this device being easily embodied in digital form.